Treatment of hydrocarbon gases



Dec. 21, 1937..

H. TROPSCH TREATMENT OF aYDRocARBoNaAsEs Filed June 22, 1934 STABILIZER RECEIVER INVENTOR CONDENSER FURNACE 1,

HA OPSCH TORNEY Patented Dec. 21, 1937 UNITED STATES PATENT OFFICE TREATMENT OF 'HYDROCARBON GASES Hans Trop sch, Chicago, Ill., assignor to Uni versal Oil Products Company, Chicago, 111., a corporation oi, Delaware Appiication'lune 22, 1934, SerialNo. 131,796

-2 Claims.-

In a more specific sense the invention has reference to a process for manufacturing gasoline boiling range hydrocarbon liquids from olefin 1 containing hydrocarbon gas mixtures by a succession of cooperative steps involving both polymerization and pyrolysis as will be hereinafter disclosed in detail.

The fixed gases produced in the cracking of petroleum have at present only a limited value as fuel for the process or forrother portions of the refinery in which the cracking plant is one unit. While the reactive olefinic content of these gases which comprises, for example, ethylene, propylene, butylenes, etc., has been utilized to some extent to manufacture, for example, hydroxy derivatives such as the corresponding alcohols and glycols, attempts to convert the gases into economic yields of gasoline have been only partly successful and it is withimproveso ments in processes of this character that the present invention is concerned.

In one specific embodiment the present invention comprises treatment oi cracked vstabilizer u gases, particularly to produce yields of gasoline boiling range liquids therefrom, by first subjecting the gas mixtures to contact with solid phosphoric acid catalysts to polymerize the olefinic constituents, cooling and separating the liquid 40 polymers from the residual gases, recracking the residual gases to produce further quantities of polymerizable olefins, separating the 3 and 4 carbon atom hydrocarbon fractions from the crack;

ing step and returning said fractions to further 45 treatment in the primarypolymerizing stage. The character oi. the invention will be developed more in detail in connection with the attached drawing which shows diagrammatically in side elevationand by the use ofconventional 50 figures the interconnected elements of a plant in which the process may be conducted. The drawing is not to scale and the process may employ apparatus involving modifications which depart therefrom to a considerable degree so 55 that the invention is not limited by the particular drawing or the description given in connection therewith.

Referring to the drawing cracked or other distillates to be stabilized may be introduced to a stabilizer unit through a line I containing con- 6 trol valve 2 to be taken by a pump 3 and dischargedthrough line 4 containing control valve 5 to pass into and through a heating element 6 suitably arranged to receive heat from a furnace 1. During passage through the heating 10 element the products are brought to a suitable temperature for eflecting their stabilization usually somewhere within the range of 225 to 275 E, the stabilizer being commonly operated at from 100 to 150 pounds per square inch. produced at a later stage in the process which is also subjected to stabilization enters line 4 from line 59. The production of this liquid materlal will be described at a later point in proper sequence.

l0 represents a stabilizer of suitable design and capacity in which. the top temperature is usually maintained at from 100 to 150 F., and the bottom temperature in the neighborhood of 325 F;, by means of the usual refluxing and reboiling operations, the details of which are omitted from the drawing as constituting no special feature of the present invention. .The heated products from the primary element pass through a line 8 containing control valve 9 to enter stabilizer ill at aipredete'rmined level. The stabilized material leaves the bottom of the stabilizer by way of line ll containing control valve l2 and flows to receiver l3 which has a fixed gas release line H containing'montrol valve I5 and a liquid draw line I6 containing control valve II. The gases vented from receiver l3 will contain only very small amounts of 3 and 4 carbon atom hydrocarbons in the normaloperation of the process. The liquid formed 'at this 40' point may be reserved for blending with the I other gasoline boiling range liquids produced at succeeding stages in the processr v The overhead vapors from stabilizer l0 pass through a line it containing control valve 19 and may conveniently be brought up to the optimum temperature for polymerizing the more reactive oleflns in the presence oi. the preferred catalyst by heat exchange with the hot products from the secondary or cracking step, receiving this heat during passage through a heat exchanger 20. In case the heat supplied by the hot cracked products is more than necessary to raise the gases to the required temperature, a certain. amount of them may be by-passed around the.

Liquid 15 I heat exchanger through line l8 containing valve H! which unites with exit line 2! containing control valve 22, the gas line then passing to polymerizer 23. The materials used in this polymerizer are of a special character and will be described in some detail.

The preferred catalytic contact materials com--- prise granular masses consisting of sized particles containing phosphoric acids adsorbed in relatively inert porous spacing or supporting materials such as, for example, ground pumice, fullers earth, clays such as bentonite and Montmorillonite, kieselguhr or diatomaceous earth, artificially prepared silica gels, etc. In making up catalysts of this character any of the acids in which phosphorus has a valence of 5 (that is.

ortho, pyro and meta phosphoric acids) may be A composite catalyst material which is effective when polymerizing gaseous olefins may be made by mixing approximately'80% by weight of orthophosphoric acid (75 to strength may be employed) with about 20% by weight of diato- 'maceous earth after which the ingredients are thoroughly mixed and ground together to produce a mass of uniform consistency, particularly in respect to the distribution of the phosphoric acid. The mixed material is next carefully heated at temperatures from about 220 to 300 C., for a considerable period of time, usually 24 to 60 hours until, due to the loss of water from both acid and adsorbent, a solid cake is produced which has the required chemical composition and physical properties. This cake is then ground out of contact with moist air to produce particles which are screened and sized for the production ofmaterial of .irom approximately 4 to 30 mesh which serves as filler for treating towers or polymerizers.

It has been found feasible to start with pyrophosphoric acid in making up the composite catalysts and in this case temperatures of from about 160 to 200 0., are employed in the primary mixing stage and while the same temperatures as those employed when starting with orthophosphoric acid are used in the heating or drying period, the time necessary is considerably shortened and may be considerably less than 24 hours. In the heating period which leads to the formation of the solid cake the original phosphoric acid is partially dehydrated and it is probable that the final contact particles contain principally pyro phosphoric acid and a small amount of the meta acid.

The solid contact materials are represented in arcade? superatmospheric of the order of from 100 to 300 pounds per square inch.

Downfiows are usually preferable on account of the washing action of the gases on the solid particles. The rate of flow is adjusted, along with the temperature and pressure to obtain a maximum of gasoline boiling range polymers.

Gases and vapors leave polymerizer 23 by way of line 21 containing control valve 28 and pass through a cooler 29 which is so regulated that preferably only gasoline boiling range liquids are condensed and substantially all of the 3 and a carbon atom hydrocarbons including propane, propylene, butane and the butenes are left in gaseous phase. A sharp separation at this point may require equipment somewhat more complicated than that-shown in the drawing and'this may be employed if necessary for the efficient operation. of the process. The fixed gases and condensed liquids enter receiveror separator 32 and the liquids may be withdrawn through line 35 containing control vailve 36 to storage or directly to blending with stabilized products. The gases from separator 32 are now preferably subjected to pyrolysis for the production of further quantities of olefinic gases, though if desired a certain portion of these gases may be withdrawn for other purposes through line 33 containing control valve 34. The bulk of the gas production passes through line 31 containing control valve 38 is in the neighborhood of pounds per square inch. The contact time in this cracking element is preferably varied so that considerable yields of higher olefins are obtained without the formation of any substantial amounts of gasoline boiling range material. The following table shows the approximate contact times which have been found favorable in most cases for thus producing higher oleflns at temperature ranges within those specifled.

Temperature vs. contact time The heated and partially cracked gases leave the heating element by way of line (3 3 containing control valve 55 and pass through heat exchanger 20 previously described wherein their temperature is reduced by indirect contact with primary stabilizer gases. The partly cooled cracked gases leave the heat exchanger by Way of line 16 containing control valve '31 and pass through a condenser i8 which may be maintained at temperatures below ordinary atmospheric to insure the effective liquefaction of the hydrocarbons of 3 and 4 carbon atoms to the molecule, since the object of this condenser is to make these compounds available in liquid form for recycling to the stabilizer and separate them from methane, ethane, ethylene and hydrogen. Line 19 containing control valve 50 represents the condenser rundown line which leads to receiver or separator 5! which has a gas release line 52 containing control valve 53 for the removal and ultimate disposal of'the lighter fixed gases mentioned and a liquid draw line 54 containing control valve 55 75 operation within the ranges specified, the results of numerous runs, both of an experimental and a plant character could be introduced to illustrate the advantages of the invention but the following example is sufilciently characteristic to indicate its possibilities.

The gas mixture charged was obtained from a stabilizer operating in connection with a residuum cracking plant, and contained ofpropylene and 9.5% of butylenes, the remainder of the components of the mixture being principally parafflnic although ethylene was present in a small percentage. The gas mixture was first treated to-polymerize the olefin content by passing it at a temperature of 410 1F., and a pressure of 150 pounds per square inch over a solid composite catalyst mixture comprising about 60% by weight ,of pyrophosphoric acid supported upon a kieselguhr base. By this operation there was produced 6 gallons of liquid per 1000 cubic feet of gas charged, corresponding to substantially complete removal by polymerization of the ole- A fins of 3 and 4 carbon atoms. The properties of the liquid produced are shown in the table bea low: v

- Properties of polymerized liquid Dissolved gas per cent 12 Gasoline fractions 100 to 437 F do 87 Higher boiling polymers do 1 Blending octane number of gasoline fraction 112 Total sulphur per cent 0.10

form additional yields of gasoline.

The residual gases from the first step of the process were then subjected to pyrolysis to produce olefins which are ultimately polymerized to I The temperature employed in the secondary cracking step is 1300 F., under a pressure of 100 pounds per square inch, a time of reaction being allowed of the order of about 6 seconds. By cooling to approximately 32 F.', the 3 and 4 carbon atom hydrocarbons comprising essentially propane, propylene, butanes, butenes, and some traces of higher boiling compounds are separated as a liq-- uid and returned to the primary stabilizer.

The total yield of gasoline produced by the foregoing operation is 9 gallons per 1000 cubic feet of stabilizer gas charged and indicates that the process is capable of considerably augmenting the yield of gasoline from the cracking process. In addition it will be noted that the octane number, of the products is of a high orderso that they are of special value for blending with gasolines which are inferior in this respect.

The foregoing specification and example have sufficiently disclosed and exemplified the invention, but neither is to be construed in the light,

of imposing undue limitations therein.

I claim as my'invention: 1. A process which comprises stabilizing cracked gasoline distillate to separate gaseous 'olefins from the gasoline, contacting the thus separated gas with a polymerizing agent to produce gasoline-boiling hydrocarbons therefrom,

separating the latter from residual gases, cracking the residual gases by heat treatment to produce polymerizable olefins therefrom, cooling the cracked products to separate the polymerizable oleflns therefrom as liquid, and supplying said liquid to the aforesaid stabilizing step whereby it is revaporized therein and passed through the polymerizing operation together with the gaseous olefins separated from said distillate.

2. A process which comprises stabilizing .cracked gasoline distillate, thereby forming a stabilizer gas consisting essentially of 3 and 4 carbon atom oleflnic and 'parafiinic hydrocarbons, subjecting the fresh stabilizer gas to a polymerization treatmentto polymerize the olefinic content thereof into normally liquid hydrocarbons, separating the latter from the residual par-.

afllnic hydrocarbons, cracking the residual parafflns to produce 3 and 4 carbon atom olefins therefrom, separating'the latter as liquid from" gaseous cracked products of lower molecular weight, and supplying said liquid to the aforesaid stabilizing step whereby it 'is revaporized therein and passed through the polymerization treatment together with the fresh stabilizer gas.

' HANS TROPSCH. 

